Critics say the 27-acre Millenium Project expansion would damage a stream and trees that have been at the site since the Civil War. And they are asking whether the cemetery should instead begin preparing for the day when the cemetery can no longer bury anyone else.

Cemetery officials plan to dedicate a new area on Thursday where more than 20,000 cremated remains can be stored. Without it, officials say the cemetery would run out of niche space by 2016. Kathryn Condon, the executive director of Army National Military Cemeteries, says if nothing is done, Arlington will run out of in-ground burial space by 2025. The Millenium Project would add nearly 30,000 grave sites, but also remove hundreds of trees.